CO₂ deep-hole presplit explosions are an important technology for enhancing gas drainage in low-permeability coal seams. In the process of a CO₂ gas explosion, the initial burst crack generated by the shock wave expands the crack tip under the splitting action of high-pressure CO₂ gas. To explore the effects of CO₂ gas explosions on crack tips, we constructed an analytical model of gas pressure attenuation at different positions based on fluid motion equations, proposed equations for crack opening and growth rates, and inverted the energy field of the whole process of CO₂ blasting. We used a test platform for the independent development of CO₂ gas explosions under experimental conditions of 1 MPa axial pressure and 2 MPa CO₂ gas pressure and a VIC-3D measurement system. We conducted the gas explosion experiments on prefabricated cracked samples with a crack length of 10 mm and width of 0.2 mm to analyze the dynamic response of the crack tip. The results showed that there were three stages in the propagation of a prefabricated crack under the action of a CO₂ gas explosion. The first stage, from 0 to 290 ms, included energy storage at the crack tip and a maximum opening rate increment of 0.0043 m/s. The second stage, from 291 to 295 ms, was rapid crack propagation with maximum opening rate increment and propagation rates of 0.1865 and 5.35 m/s, respectively. In the third stage, from 296 to 309 ms, the crack tip propagated slowly, the maximum opening rate increment and growth rates were 0.0969 and 5.81 m/s, respectively, and the crack arrest coordinates were 4.57 and 35.28 mm. The experimental study verified the accuracy of the calculation model, proved that CO₂ gas promotes the growth of crack tips, explained the spatiotemporal evolution mechanism of the CO₂ explosion process, and provided experimental support for subsequent research related to explosions.

Considering the problems related to hydrofracturing, CO₂ fracturing is a more effective way to enhance the permeability of coal seams. Conventional research has focused on the dynamic behavior of coal and rock under CO₂ fracturing. There is a lack of quantitative descriptions of the fracturing stages. Therefore, CO₂ fracturing experiments were carried out with coal-like material at several pressures. The maximum principal strain field was obtained by analyzing the surface images of the specimens. Nine characteristic parameters of typical grayscale and texture images were calculated from the strain field. The correlation between the maximum principal strain and the characteristic parameters was examined using gray relational analysis, and the effects of pressure on those parameters were investigated. We obtained some interesting results, for example, the standard deviation increased from 50 to 100, and kurtosis decreased from -1.0 to -1.5 with the fracturing pressure. The thresholds of the characteristic function F at different fracturing stages were determined, too. This research provides a basis for designing the drilling hole location and determining the millisecond delay of multihole fracturing, as well as for automatically dividing the fracturing stages with artificial intelligence based on the maximum principal strain field.

The bore hole is sealed from a sealing hole: the surrounding coal fracture permeability and grout cementation form a new consolidated body and coal material. In this paper, the characteristics of the macroscopic compressive strength, microscopic interface bending, porosity, and fractal dimension of the consolidated body were studied, and the structure strength relationship between loading rates, porosity, fractal dimension, and uniaxial compressive strength (UCS) was established. The results show that the loading rates had a great and consistent effect on the macro- and micro-mechanical properties of the consolidated body. Macroscopically, in the range of 0.1~0.4 mm/min, the UCS and elastic modulus of the solidified body increased with the increase in the loading rate, and there was a critical loading rate (η = 0.4 mm/min). At the microscale, with the increase in loading rates, the interface bending phenomenon, porosity, fractal dimension, and UCS of the grout and coal were consistent, showing a trend of increasing first and then decreasing. The fractal dimension was linearly correlated with the UCS and porosity. The loading rates, porosity, fractal dimension, and UCS had a multivariate nonlinear regression distribution.

Herein, we report a novel solvent-induced fabrication method to synthesize a perovskite thin film on flexible substrates. The high-quality CH₃NH₃PbI₃ (MAPbI₃) thin film is successfully fabricated, which is applied to prepare the stable flexible photodetector (PD). Compared with the reported results, this method achieved a low-temperature and low-cost perovskite thin film fabrication process on a flexible substrate. The constructed MAPbI₃ layer possesses the advantages of being highly crystalline, uniform, and compact in a large area. The flexible PD based on the as-prepared perovskite thin film exhibits excellent performance and long-term stability. The EQE and R of the flexible PDs reached 8 × 10²% and 3.6 A/W, respectively. At the same time, the flexible PDs still showed superior stability and high performance after 15 days of continuous working. The presented high-quality perovskite thin-film fabrication method and high-performance flexible perovskite PDs are expected for application in the development of novel optoelectronic devices.